Rubber compositions containing unsubstituted rosin amines



Patented Dec. 20, 1949 ZAWLQH RUBBER COMPOEiIl'lIiDNS @ONINING UNSUBS'EHTU'EED HtOSIN Lyle U. Amber-g, Wington, Hercules Powder @ompany, a corporation oi liielaware Dell, assignor to Wilmington, Del,

No Drawing, accusation time 11, rate, senor No. eraser l2 Claims. till. mill-$27) This invention relates to rubber compositions and, more particularly, to rubber compositions containing a rosin derivative.

It has been known that ordinary rosin may be used in the compounding oirubbei". According to methods frequently employed in the art,

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function of the rosin is to soften, or plasticlze,

the rubber composition on the rolls of the mill, rendering the composition more susceptible to mechanical working, and thereby rendering the milling process less expensive and more efl'lcient. Although the use of ordinary rosin is advan tageous from this point of view, the presence oi rosin in the final rubber composition imparts to the latter certain. undesirable characteristics, one of the most important of these being that the rubber composition exhibits considerable reactivity toward atmospheric oxygen.

It also is well known to use amines and, dierivatives of amines with rubber during the-prom ess of vulcanization. Such amines and their derivatives serve a useful purpose as accelerators, activators of accelerators, and, in a few instances, as antioxidants. Aniline, for example, was once widely used as an accelerator of vulcanization but has been abandoned largely because of its toxicity. At the present time amine derivatives such as diphenyl guanidine, di-o-tolyl guanidine, thiocarbanilide, thiuram disulfides, N-cyclohexyl- 2-benzothiazole sulphenamide, piperidinium pen tamethylene dithiocarbamate, aldehyde-amine and ketone-amine condensates are widely used in. vulcanized rubber products. The need has long been felt, however, for a material which would combin the plasticizing effect of rosin with the accelerating and activating effects of the various amines and their derivatives.

In accordance with this invention, it has been found that rubber compositions having valuable and improved properties may be obtained if there is used as a compounding agent a rosin derivative selected from the group consisting of an amine derived from a rosin and a weak organic acid saltof an amine derived from a rosin. In accordance with this invention, compositions may be prepared which, in the unvulcanized state, possess 41c improved processing properties such as improved plasticity, softness, and tack, and which cure more quickly to vulcanizates with improved properties such as increased resistance to heat em" brittlement and resistance to oxidation. If the rubber is to be vulcanized, it is compounded with a vulcanizing agent and an amine derived from a resin, or a weak organic acid derived from a rosin, and then vulcanized according to standard procedures. In addition to the rosin amine and the vulcanizing agent, there may be employed fillers, pigments, activators, and similar materials customarily emplayed by the art to modify the properties of the vulcanized composition or to facilitate its preparation, in such kind and quantity as may be necessary to obtain the particular desired qualities in the flnalproduct.

In order to present certain specific embodiments of the invention which has been described broadly in the preceding paragraphs, the following table contains examples of formulations which may be employed in accordance witlrthis invention. In the examples shown by this table and in the examples thereafter, all quantities of ingredients are in parts by weight unless otherwise specified.

Table i Example Number GR-S synthetic rubber Stearic acid Zinc oxide Captor Hydroabletylamina... N wood rosin .l

The following designations apply to the mate rials used in the compositions of Table l: GR-S synthetic rubber (Government Standard copolymer of parts butadiene and 25 parts styrene), stearic acid (Stearex beads), zinc oxide (XX Red 4), carbon black (channel black), sulfur (micronized), Santocure (N-cyclohexyl-Z-benzothiaaole sulphenamide), Captax (2-mercaptobenzothiazo e.

In the preparation of the compositions of Table I, a master batch was first prepared starting with the total synthetic rubber required for the three examples. The master batch was milled eight minutes while circulating cool water through the rolls, and the materials common to all of the examples were added in the following salt of an amine order: stearic acid, zinc oxide, carbon black, and sulfur. After each material was incorporated, the sheet was twice cut in from each side twothirds of the way across. After all of the sulfur was in, the sheet was cross-cut two-thirds of the way across twelve times from each side and then out off and end-rolled twelve times. The material was then allowed to form a band and sheeted E. The master batch then was divided into three equal portions, each portion was placed separately on'cool rolls, and the remaining components necessary in each example were. added. After thorough mixing on the rolls, the completed compositions were sheeted ofl. and allowed to stand overnight. Suitable portions were cut out of each sheet and cured at 280 F. for 10, 30,'

60, and 90 minutes, respectively.

It was found that the rubber prepared according to Example 1 cured more rapidly than either a corresponding rubber containing no hydroabietylamine or one containing no N wood rosin or hydroabietylamine. In the case of Example 2, it was found that the presence of the hydroabietylamine reduced the time required to efiect vulcanization as compared to other rubbers activated by a mercaptobenzothiazole. Example 3 showed that hydroabietylamine was eflective as the sole accelerator during vulcanization and also that the presence of the amine produced a softer unvulcanized stock with improved building tack.

Table II Example Number 4 5 6 7 -S thetic rubber 250 250 260 300 gt gari c id 2.5 2.5 2.6 3 Santocure 4. 5 4. 5 4. 5 6 4 Zinc oxide 12. 5 12. 5 12. 5 l5 Precipitated salt of ,hydroabietylamine and hydrogenated rosin. Fused mixture of hydroabietylamine 20 parts) and hydrogenated rosin 5805mm) 25 Fuse mixture of dehydroabietylamine (25 parts) and dehydrogenated rosin (75 parts). 25 H dr ted rosin 22,5 Hydroabietylamine..- 7.5 Carbon biacln. 150 Sulfur 6 The compositions set forth in Table .II were formed by running each synthetic rubber sample through milling rolls once at 100 F. and allowing The composition of Example 5 was quite comparable to that of Example 4 even though a much smaller proportion of hydroabietylarnine was present in comparison to the amount of hydrogenated rosin. The composition shown by Example 6 gave a vulcanizate having good building tack and resistance to extended heat embrittlement. Example 7 indicated thatthe hydroabietylamine and the hydrogenated rosin need not be in the form of a fused mixture in order to obtain the beneficial effects since, in Example 7, the two rosin components were added separately during the compounding procedure.

Table III Example Number 8 9 10 Crude natural rubber (No. l Smoked Sheets) 300 (1)0 :00 Santocure 1. 98 1. 98 l. N Carbon black. 1150 160 150 Stearic acid. .4.-. 9. 75 9. 76 9. 75 Zinc oxide 15 16 i5 Fused mixture of hydroabietylamine parts) and hydrogenated ros n parts). 6 Hydrogenated lOSlll 4. 6 Hydroabietylamine... l. 6 N wood rosin amine. 1.5 N wood rosin 4. 8 ur 7. 6 7. 6 7. 5

thickness. The sheets were allowed to stand overnight. Suitable portions were cut out of each sheet and cured at 280 F. for 45, 60,,and minutes, respectively. Each portion then was cut into dumb-bell samples with a type "C" die a sheet to form on the front roll. Cold water I was then passed through the rolls and milling allowed to continue for eight mintues, the band being out once each way each minute. The stearic acid, Santocure, and zinc oxide were added in that order, the band being out between the addition of each reagent. The next stepin each example was the addition of the particular rosin amine composition. Each hand then was cross-rolled six times, the mill opened to form a low bead, and the carbon black added. When.

all of the carbon black was in, the sulfur was added without cutting. The compounded sheet was then cross-cut twelve times each way and cross-rolled twelve times. The rubber sample, after cooling to room temperature, was refined five times through tisht'roils and then was sheeted off to give a sheet of about 0.075 inch in thickness. After standing overnight, samples of each material were cured for 30, 60, 90, and minutes, respectively, at 280 F.

The composition of Example 4 cured rapidly to a vulcanizate' with good tensile properties and outstanding resistance to heat embrittlement.

(A. S. T. M. No. D412-41) One-half of the specimens prepared from each sample were aged for 24 hours at 212 .F. in an air oven and tested simultaneously with the unaged specimens on a Scott L6 rubber tester, jaws separating 20 inches per minute.

The natural rubber vulcanizates prepared according to Examples 8, 9, and 10 had good tensile properties and outstanding resistance to heat embrittlement. The properties of elongation at break and modulus of elasticity also were entirely satisfactory.

The process in accordance with this invention is carried out in the presence of an amine derived from a rosin or a weak organic acid salt of an amine derived from a rosin. Any rosin may be employed to prepare the amines which are used in the process of this invention. The amines may be derived, in other words, from various resins and modified rosins. Thus, in place of the N wood rosin amine used in Example 10, there may be used an amine prepared from anywood or gum rosin or the pure acids contained therein such as abietic and pimaric acids. The modified rosin amines shown by the examples have been dehydroabietylamine and hydroabietylamine, but the amines derived from other modified rosins such as polymerized rosin, heat-treated rosin, isomerized rosin, and the like, also are operable. The modified rosin amines may bederivedmot only from the pure acids such as dehydroabietic,

, carrier, such as alumina, fibrous asbesto dlhydroabietic, and tetrahydroabietic contained in the various modified roslns, but also from materials containing these acids such as dehydrogenated rosin, hydrogenated rosin, etc.

Hydroabietylamine and dehydroabietylamine, for example, are ultimately derived from hydrogenated and dehydrogenated rosin, respectively. The hydrogenated rosin is prepared by contacting a natural rosin or rosin acid in a fluid state with hydrogen in the presence of an active hydrogenation catalyst, such as activated nickel, Raney nickel, copper chromite, cobalt, platinum, platinum oxide, and the like. Many variations of the hydrogenation reaction may be utilized. a

The .dehydrogenated rosin is obtained by the dehydrogenation or disproportionation oi natural rosin or a rosin material containing a substantial amount'of a natural rosin, such as gum or wood rwin. The dehydrogenation or disproportionation reaction is carried out by contacting the rosin or rosin material at an elevated temperature, in the absence of added hydrogen, with an active hydrogenation catalyst, such as palladium, platinum, nickel, copper chromite, eta, to effect a dehydrogenation or disproportionation reaction. The catalysts may be supported on a s or activate charcoal.

The natural rosin may be refined by any means, such as by crystallization, by means of a selective solvent such as furfural or phenol, or by an adsorbent earth such as fullers earth, prior to its use in the preparation of an'amine derived from rosin, or prior to its use in the preparation of a modified rosin, such as hydrogenated or dehydrogenated rosin. The hydrogenated, dehydrogenated, or other modified rosin also may be refined, as by distillation or other means prior to their use in the preparation of the corresponding amines.

The next step in the transformation of any of the resins or acids thereof to the corresponding mine is the conversion of the rosin material to the corresponding nitrile. The reaction may be carried out by passing gaseous ammonia into 7 the molten rosin material and vaporizing the water as fast as it is formed in order-to remove the water from the reaction mixture. The nitriles also may be formed by heating the rosin material with ammonia in the presence of a do hydration catalyst. The nitriles then should be purified by neutralization and distillation before subjecting them to hydrogenation in order to produce the corresponding amines.

The hydrogenation of the nitriles may be carried out either in the presence or absence of ammonia, since the presence of ammonia is not necessary to prevent the formation of secondary amines. Any active hydrogenation catalyst, such as nickel, cobalt, Raney nickel, Raney cobalt, active platinum, palladium, palladium on carbon, or reduced platinum oxide, may be used in the hydrogenation reaction. The nitriles to be hydrogenated should be essentially free of acids to prevent destruction of the catalyst and also to prevent color in the product and a lower I yield. The hydrogenation of the nitrile may be carried out in a batch or continuous process, and the amine may be recovered and purified by conventional procedures.

The amine prepared from the nitrile of rosin is a mixture of the amines Of the various rosin acids present in rosin. That from hydrogenated rosin is a mixture of dihydroabietylamine and tetrahydroabietylamine, since hydrogenated rosin is a mixture 01' hydrorosin acids. The proportion of dihydro derivative to tetrahydro derivatlve is dependent upon the degree of hydrogenation or the rosin in the pre ration of the hydrogenated rosin. If either the pure dihydroabietylamine or tetrahydroabietylamine is tiesired, they may be separated from the mixture or they may be prepared by the hydrogenation of the corresponding dior tetra-hydroabietonitrile. in the same way, pure dehydroa i yh amine m y be prepared by the hydrogenation of Pure dehydroabietonitrile. It is desirable that the amine used be or high purity in order to ob-= taih maximum emciency, although products con-- taining some nitrile are operable.

The examples have shown various ways in. which the rosin amines may be used in accordance with this invention. The amine may be utilized as in Example 3 as the sole softening and acceier atine agent or it may be used as in Example 2 in conjunction with conventional accelerators. Additional softening agents such'as the N wood rosin shown in Example 1 also may be added to the composition. As shown in Examples t to 10, it may be desirable to use the rosin amine in conjunction with the particular rosin compound from which it ultimately was derived, but it is not necessary that the particular rosin compound from which the amine was derived be utilized. Either dehydroeenated rosin or N wood rosin, for example, could be used in preparation or a precipitated salt of hydroabietylamine which would be comparable to the precipitated salt used in Example 4. In general, when using a combine tion of a rosin amine and a rosin, these components may be added separately during the come pounding operation or may be added in combi nation in the form of a precipitated salt of the amine and the rosin compound or as a fused mixture thereof. The fused mixture takes the form or a salt 01 the amine and the rosin. Although the fused mixtures shown in Examples 5 and d were in the ratios of :80 and :75 rosin amine: rosin acid, the ratio may be varied from 12.5:ii7ii to iillzfiii. 0n the basis of performance and cost, however, the most desirable ratio is 75:25.

Although Examples 4, 5, 6, and 8 have shown only those amine salts prepared by precipitation or fusion oi the amines with certain resins, which are weak organic acids, other such acidic incterials may be utilized in preparation of the amine salts operable in accordance with this invention. Exemplary of such materials are polymerized rosin, heat-treated rosin, isomerized rosin, the 55 pure acids contained in such rosin, and the like.

According to Holleman (A Textbook of Organic Chemistry by A. F. li-lolleman, 5th English edition (1920), .l'ohn Wiley iii Sons Inc, page 11.7) "the strength of acids depends upon their degree or m ionization, strong acids undergoing considerable and weak acids but slight ionization. The degree of ionization is expressed in terms of dissociaiton constants. The dissociation constant of stearic acid 01' the examples, for example, is 3i.7 10-, at N C. or 2.6 lllat C. (N. P. Datta, Journal of the Indian Chemical Society, vol. 16, No. 11,

November 1939, page 573). Salts of the amines also may be prepared from such weakly acidic materials as the 2 some of the examples as an accelerator. The rosin amines all form salts with mercaptobenzothiazole, and this aiiords a simple means 01* introducing both the amine and an additional erator simultaneous! The amine salts of -mercaptobenzothiazole used in 1 accel- I y to the rubber composition. mercaptobenzothiazole act as:

7 efiicient accelerators of vulcanization, giving tire tread stocks which are improved in resistance to hot flex out growth after extended accelerated ing. 'lhe amount of amine utilized, in preparation of the rubber composition may be from about 0.05 to about 20% based upon the weight of the rubber. Upon this basis the preferable amount is from about 0.1 to about 10%. When the amine is used in the form of a salt of a weak organic acid, the amount of the salt will be that which will be equivalent to the desired amount of amine, calculated as the free amine. amine used will generally vary depending upon the type of rubber, the nature of the composition,

the function of the rosin amine, and the properties desired in the product. In general, the synthetic rubbers such as those derived from the copolymerization of butadiene and styrene will require somewhat larger amounts of the rosin amine than does natural rubber, since synthetic rubbers usually necessitate a stronger acceleration during vulcanization.

The examples have shown the use ofvarious rosin amines, or their salts with weak organic acids, in the compounding of natural rubber and GR-S synthetic rubber, the latter being a copolymer of butadiene-llli and styrene. The process of this invention may be applied, however, to

. other synthetic rubberlike polymers, such as those prepared by polymerizing dioleflns, halogenated derivatives of dioleflns or other substituted diolefins, or by copolymerizingdioleflns with other compounds containing a vinyl group, such as styrene, acrylic acid esters, and acrylic acid nltrile. More specifically, the rubberlike polymers may be those obtained by polymerizing the conjugated butadiene hydrocarbons, butadiene and its derivatives, such as isoprene, dimethyl butadiene and chloroprene, or by copolymerizing, for example, butadiene and styrene or acrylonitrlle, or isoprene and styrene or acrylonitrile. The commercial synthetic rubbers to which the process of this invention is particularly applicable are: GR-S (butadlene-styrene copolymer), GR-N (butadiene-acrylonitrile copolymer), and GR-I (butadiene-isobutylene or isoprene-isobutylene copolymer).

The usual fillers, reinforcing agents, antioxidants, vulcanizers, extenders, plasticizers, softeners, processing aids, as well as other activators and accelerators well known in the preparation of The amount of fur. However, in certain cases, selenium or tellurium may be employed either alone or in conjunction with sulfur in order to obtain desirable modifications of the characteristics of the composition in respect to the vulcanization process. In the event that the traces of ,these vulcanizing agents may be objectionable in the vulcanized product, a peroxide vulcanizing agent, such as benzoyl peroxide, may be employed.

As .a means for obtaining vulcanization of the composition at lower temperatures or for increasing the rate of vulcanization, suitable accelerators may be employed. Accelerators which are familiar to the art are, in general, satisfactory. Thus, in place of the accelerators employed in the examples, there may be employed accelerators, such as di-o-tolyl guanidine, ethylidine guanidine, hexamethylenetetramine, methylene aniline, tetramethylthiuram disulfide, thiocarbanilide, diphenylamine, diphenyl guanidine, tetramethylthiuram monosulflde, triethyltrimethylenetriamine, triphenyl guanidine, and the like. The effects of these various accelerators and of accelerators which are equivalent thereto, upon the vulcanization of the composition and upon its properties after vulcanization may vary somewhat, in a manner known to the art, and thereby provide means for controlling certain of the properties of the vulcanized product. Although the additional control of the characteristics may be desirable in certain circumstances, in general the use of mercaptobenzothiazole or of N -cyclohexyl- 2-benzothiazole sulphenamide has been found to be preferable. I

In general, because of the marked stability of the present compositions to the efiects of exnatural rubber and synthetic rubber compositions,

may be employed in accordancewith this invention. Thus, the fillers which may be employedare, for example, aluminum flake, antimony sulfide, asbestos, barium sulfate, cadmium sulfide,

appropriate grades of carbon black, chromic oxide, clay, such as bentonite, cotton linters, iron oxide, lime, litharge, lithopone, magnesium carbonate, or oxide, silica, slate flour, talc, titanium oxide, whiting, zinc oxide, zinc sulfide, or the like. Zinc oxide, reinforcing grades of carbon black, and the like, may be employed as reinforcing agents. Preferably, a mixture of suitable fillers andreinforcing agents is employed to give to the compositions the particular properties which may be desired. Thus, a mixture of zinc oxide and carbon black may be employed in the manner illustrated by the examples. Suitable pigments, such as ultramarine, vermillion, or the like may be empuloyed to impart to the composition a desired color.

The vulcanizing agent which is employed in accordance with this invention preferably is sulposure to the atmosphere, the use of powerful antioxidants is not so essential as in the case of rubber compounded with ordinary rosin. However, in the event that it is desirable further to decrease the effects of oxidation on the rubber, suitable antioxidants may be added. Suitable antioxidants are, for example, diphenylamine, aldo-a-naphthylamine, diphenylethylene diamine, phenyl-a-naphthylamine, or phenyl-p-naphthylamine. In case a commercial synthetic rubber to which antioxidants normally are added during preparation is employed, the amount of antioxidant added during the compounding of the present compositions may be decreased suitably.

The use of the various fillers, antioxidants, and the like hereinbefore mentioned is well understood by those skilled in the art and, in general, these compounding ingredients may be employed in the manner customarily employed by the art.

Vulcanized products prepared in accordance with the present invention have been found to be of particular value as tire treads. The compositions also are of value in the manufacture of other articles, such as tire carcass stocks, inner tubes, rubber hose, rubber-lined hose, footwear, electrical insulator goods, molded rubber articles, and the like. The improved processing characteristics, such as plasticity, of the present compositions prior to vulcanization facilitate significantly their compounding as well as subsequent operations such as extrusion molding and the like. During vulcanization, the present compositions exhibit a faster rate of cure than do comparable compositions containing no rosin amine. The resin amine, during the vulcanization process, may serve as the sole accelerator or as an activator of another accelerator or as a means of overcoming the cure-retarding efiect of rosin softeners. The improved characteristics of the Patent 18:

a ienate vulcanized product are apparent in their in creased tensile strength, increased resistance to oxidation, increased resistance to embrittlement upon aging. improved compression set, and improved heat-buildup properties.

What I claim and desire to protect by Letters 1. A rubber composition comprising a conjugate diolefln polymer and a material of the group conamine, the weight of said rosin amine in the composition amounting to about 0.05 to about 20% of the weight of said conjugate diolefln polymer.

3. A rubber composition comprising a conjugate diolefln polymer and a salt of an unsubstituted rosin amine and an organic acid having a. dissociation constant equal to about 1.7xat 35 C. or 2.6X10- at 50 C., the weight of said rosin amine in the composition amounting to about 0.05 to about of the weight of said conjugate diolefln polymer.

4. A rubber composition comprising a conji1- gate dioiefln polymer and a salt of an unsubstituted dehydrogenated rosin amine and an organic acid having a dissociation constant equal to about 1.7x10- at C. or 2.6x 10- at 50 0., the weight of said rosin amine in the composition amounting to about 0.05 to about 20% of the weight of said conjugate diolefin polymer.

5. A rubber composition comprising a conjugate diolefln polymer and a. salt of dehydroabietylamine and an organic acid having a dissociation constant equal to about 1.'7 10- at 35 C. or 2.6X10- at 50 C., the weight oi. said dehydroabietylamine in the composition amounting to about 0.05 to about 20% of the weight of said conjugate diolefln polymer.

8. A rubber composition comprising a coniugate dioleiin polymer and a salt of an unsubstituted hydrogenated rosin amine and an organic acid having a dissociation constant equal to about 1.7x10-' at 35 C. or 2.6x10- at 50 C., the

weight of said rosin amine in the composition amounting to about 0.05 to about 20% 01. the weight of said conjugate diolefln polymer.

7. A rubber composition comprising a coniugate diolefln polymer and a salt or hydroabietylamine and an organic acid having a dissociation constant equal to about 1.7)(10 at 35 C. or

2.6)(10 at (3.. the weight of said hydro-' abiethylam ne in the compositi amounting to about 0.05 to about 20% oi the weight of, said conjugate diolefln polymer.

8. A rubber composition 'zuimprisine a eopolyuser of butadiene-1,3 and styrene and a salt oi.

dehydroabietylamine and an organic acid having a dissociation constant equal to about 130010 at 35 C. or 2.6 10 at 50 C., the weight of said dehydroabietylamine in the composition amounting to about 0.05 to about 20% of the Weight of said copolymer.

9. A rubber composition comprising natural rubber and a salt of hydroabietylamine and an organic acid having a dissociation constant equal to about 1.7)(10' at 35- C. or 2.6 10 at 50 (3., the weight of said hydroabietylamine in the composition amounting to about 0.05 to about 20% oi the weight of said natural rubber.

10. A vulcanized rubber composition obtained by vulcanizing a mixture comprising a conjugate diolefin polymer and a material of the group consisting of an unsubstituted rosin amine and a salt of an unsubstituted rosinamine and an organic acid having a'dissociation constant equal to about 1.7 10 at 35 C. or 2.6 10- at 50 0., the weight of said rosin amine in the mixture amounting to about 0.05 to about 20% of the we ght of said conjugate diolefin polymer.

11. A tire tread stock comprising a conjugate diolefln polymer, a vulcanizing agent, a reinforcing agent, and a material of the group consisting of an unsubstituted rosin amine and a salt of an unsubstituted rosin amine and an organic acid having a dissociation constant equal to about 1.7 10--' at 35 C. or 2.6x1tH at 50 0., the weight of said rosin amine in the stock amounting to about 0.05 to about 20% of the weight of said conjugate diolefln polymer.

consisting of an unsubstituted rosin amine and a salt of an unsubstituted rosin amine and an organ c ac d having a dissociation constant eoual to about 1.7 10 at 35 C. or 2.6X10- at C., the weight of said rosin amine in the composition amounting to about 0.05 to about 20% of the weight of said conjugate diolefln polymer.

LYLE O. AMBERG.

REFERENCES CITED The following references are of record .In the iile of this patent:

UNITED STATES PATENTS Pragofl June 5, 1945 

